Loudspeaker



1956 J. F. ROESEL, JR, ETAL 3,

LOUDSPEAKER Filed Dec. 3, 1962 4 Sheets-Sheet l INVENTORS l John FRoesel,Jr.,Richurd A. Whisnont and William L. Wright. BY?

a I b ATTORNEY Aug. 23, 1966 J. F. ROESEL, JR. ETAL 3,253,672

LOUDSPEAKER Filed Dec. 5. 1962 4 Sheets-Sheet 2 A g 1966 J. F. ROESEL,JR. ETAL LOUDSPEAKER 9mm, o mm mm, 2 o m my mN Sm United States Patent3,268,672 LGUDSPEAKER John F. Roesel, .Iiu, De Land, Fla, Richard A.Whisnant, Spartanburg, S.C., and William L. Wright, Monroeviile, l a.,assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., acorporation of Pennsylvania Filed Dec. 3, 1962, Ser. No. 241,590 7Claims. (Cl. 179115.5)

This invention relates to an acoustic device or transducer and moreparticularly to a magnetic loudspeaker for reproducing sound.

In order to reproduce relatively low frequency sound signals, havingfrequencies of 20 to 200 cycles, it is necessary to employ a loudspeakerwhich has a relatively large radiating diaphragm that is relativelystiff. Due to the fact that the diaphragm of such speakers is relativelylarge and relatively stiff, the reproduction by such a loudspeaker ofsound having a frequency above approximately 3 to thousand cycles, isrelatively inefiicient. Consequently, the reproduction of theserelatively high frequencies by such a loudspeaker is not consideredadequate and an additional speaker generally called a tweeter isemployed. Frequently, the tweeter is a completely independent speakerhaving its own voice coil and its own diaphragm which is connected tothe main speaker or woofer merely by an electrical connection of acrossover network. With such a crossover network the woofer reproducesthe low notes whereas the tweeter reproduces the high notes. Other meanshave been employed, such as attaching a relatively small second conediaphragm to the original Woofer cone diaphragm so that the smaller coneforming a part of the relatively large conical diaphragm will increasethe efliciency of the reproduction of the relatively high notes.

In copending application entitled Loudspeaker, Serial No. 244,234, filedDecember 3, 1962, in the names of John F. Roesel, Richard A. Whisnantand William L. Wright, there is disclosed a loudspeaker having a largerelatively thin radiating diaphragm the peripheral edges of which definea rectangle. The voice coil for this radiating diaphragm is rectangularin shape and has a connection to the diaphragm which defines arectangle. The magnetic assembly provides two linear air gaps for thelongitudinal sides of the rectangular voice coil. This provides thedriving force for adequately reproducing relatively low notes.

Accordingly, it is an object of the present invention to provide a newand improved loudspeaker.

It is also an object to provide a new and improved loudspeakeridentified as a tweeter to adequately reproduce frequencies above 4 or 5thousand cycles.

A further object is the provision of a loudspeaker commonly known as atweeter which is mounted on and structurally integral with a woofer.

The features of the present invention include a new and improvedmagnetic assembly for a loudspeaker which provides an air gap for awoofer and integral with this magnetic assembly provides a magnetic airgap for a voice coil of a tweeter.

Other objects and various features will become apparent from the readingof the following specification and examination of the accompanyingdrawings, in which:

FIGURE 1 illustrates a front isometric layout view of a loudspeakerembodying the invention;

FIG. 2 illustrates a partial isometric layout of the voice coil,diaphragm and magnetic assembly of the loudspeaker illustrated in FIG.1;

FIG. 3 illustrates a rear view of the loudspeaker illustrated in FIG. 1;

FIG. 4 illustrates a crosssectional view taken along plane IVIVillustrated in FIG. 3

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FIG. 5 illustrates a cross-sectional view of the loudspeaker taken alongthe plane V-V of FIG. 3;

FIG. 6 is an enlarged cross-sectional view of the portion of the Viewtaken along lines VI-VI of FIG. 3;

FIG. 7 is a front view taken along lines VIIVII in FIG. 6; and

FIG. 8 illustrates the winding of the voice coil shown in FIGS. 2through 5.

In the above mentioned patent application entitled Loudspeaker, SerialNo. 244,234, filed December 3, 1962, in the names of John F. Roesel,Richard A. Whisnant, and William L. Wright, there is disclosed aloudspeaker similar to the loudspeaker illustrated in the presentapplication. As illustrated in the drawings, this loudspeaker includesgenerally a rectangular frame 50 shown in FIG. 1, and a lightweightrelatively low Q diaphragm 20 which is suspended from the frame 50 bysuspension means 30. Mounted on the rear of the rectangular diaphragm 20is a rectangularly shaped voice coil assembly 4% to which the amplifierof the sound system is connected to drive the diaphragm 20. The voicecoil assembly is connected to the diaphragm 20 by a connecting basemember which defines the non-circular rectangular area for driving thediaphragm. Also mounted on the frame is a magnetic assembly whichprovides two linear parallel air gaps which are adapted to receive thetwo lengthwise sides of the voice coil assembly 40 to provide two linearair gaps for the voice coil necessary for vibrating the diaphragm 20, inresponse to audio signals being applied to the voice coil assembly 40.

The magnetic assembly to provide linear air gaps for the voice coil inthe loudspeaker illustrated in the aboveidentified patent application aswell as illustrated herein, includes bar type rectangula-rly shapedmagnets and pole pieces which provide the linear air gaps between thepole pieces. As stated above, it is frequently desirable to employ ahigh frequency tweeter when utilizing a relatively large radiatingdiaphragm woofer. In the present invention two of the rectangularlyshaped pole pieces of the magnetic assembly are extended which polepieces are conducting opposite magnetic polarization. An aperture isprovided in one of the pole pieces whereas the other pole piece has apole piece extension which extends into the aperture of the other polepiece. A tweeter is employed having a voice coil which is positionedwithin the air gap defined by the extension of the two pole pieces.Further, the diaphragm of the tweeter is suspended or mounted on thepole piece having the circular aperture therein.

More specifically, the diaphragm 20 is constructed of a foamed cellularplastic which is sandwiched between two relatively thin strong layers ofsuitable material such as a fibrous woven Dacron. The method ofproducing this diaphragm is described in detail in the above-mentionedpatent application. The shape of the diaphragm Ztl is shown in FIG. 1with FIG. 4 illustrating a cross-sectional view of the length of thediaphragm and FIG. 5 illustrating a cross-sectional view of the width ofthe diaphragm. As shown in these figures the diaphragm Z0 is planarorrelatively flat and is rectangular in shape. The diaphragm 20,rectangular in shape, has its edges tapered to a thinner portion forconnection to suspension means 30. It will be seen in FIG. 1 that thetapered linear edges 21, 22, 23 and 24 of the diaphragm 20 define arectangular edge which, as shown in FIG. 1, has rounded edges at thecorners. These linear tapered edges are integral with or connected tosurround suspension means 30. A cross section of the linear portions ofthese surround is illustrated in FIGS. 4 and 5. As illustrated in FIGURE1, the upper tapered edge 21 of the diaphragm is integral with orconnected to a linear disposed surround 32. As shown in FIG. 5, thelinear edge 21 is connected to but integral with surround 32 having anoutwardly extending linear roll 32b and an inwardly extending roll 32a.Likewise, the linear edge 22, as shown in FIG. 4, is integral with orconnected to linear disposed surround 33 having an outwardly extending180 roll 33b and integral therewith a linearly disposed inwardlyextending roll 33a. Likewise, the lower horizontal edge 23 of diaphragmis connected to surround 34 having an outwardly extending lineardisposedroll 34b and a linearly disposed inwardly extending roll 34a. Also, thevertically disposed edge 24 of diaphragm 20, as shown in FIG. 4, isconnected to surround having an outwardly extending 180 roll 35b whichis integral with an inwardly extending linearly disposed 180 roll 35a.Extending outwardly from and coplanar with the tapered edge of thediaphragm 20 are coplanar fastening portions 32c, 33c, 34c and 350. Aswill be explained later these portions are connected to the frame 50 formounting the diaphragm thereon.

Mounted on the rear surface of the diaphragm 20, is, as shown in thedrawings, a voice coil assembly which is secured by glue or some othersuitable means to the rear planar surface. The voice coil assembly 40includes, as shown in FIG. 2, a channel coil support 41 for supporting avoice coil 42. The support 41 has two rectangularly shaped horizontallydisposed parallel supporting members 41a and 41b which are connected toa rectangular base 410. The edges of 41a and 41b are integral with therectangular base 410 and perpendicular thereto. Further, a supportingstrip 41d, shown in FIGS. 4 and 5, is constructed midway between theends of supporting members 41a and 41b to prevent vibration of thesupporting members 41a and 41b. The members 41a, 41b, 41c and 41d areconstructed of some suitable relatively light metal such as aluminum andare relatively thin so that the voice coil can be placed into arelatively thin air gap. The windings of the rectangular voice coil 42are wound around the outer surfaces of the supporting members 41a and41b.

The rectangular voice coil 42 includes parallel longitudinal voice coilsections 43 and 44 with parallel voice coil end sections 45 and 46.Sections 43 and 44 are bonded by some suitable adhesive or glue forattachment to support member 41a and 4112, respectively. Voice coilsections 43 and 44 extend beyond the ends of support members 41a and41b, respectively, so that voice coil sections 45 and 46 are positionedoutwardly from the ends of support members 41a and 41b. The voice coil42 is centered lengthwise on the coil support 41. The voice coil 42 iscomprised of one or more layers of electrically conductive wire whichare coated with some suitable electrical insulating material. The wireis wound in a helical fashion in a rectangular pattern, such asillustrated in FIG. 8. If two layers are used the wire is wound backover the first layer of wire in a helical fashion in a rectangularpattern and both the voice coil leads 48 are on the same end of thevoice coil. The voice coil, after it is wound is encapsulated with anadhesive or bonding material to make the voice coil 42 rigid and preventmovement of wires in the voice coil. The rectangular driving base member410 is secured to the rear surface of the diaphragm 20 by some suitableadhesive. In the embodiment illustrated in FIG. 4, the base 410 of thevoice coil 40 is secured to diaphragm 20 midway between and parallel tothe top and bottom of the diaphragm 20 and is horizontally disposed.

The driving base member 41c of the voice coil 42, being non-circular orrectangular and forming a relatively large planar connection withdiaphragm 20, provides a uniform non-critical drive to the diaphragm 20when actuated by signals applied to the voice coil 42. Being rectangularin shape, the supporting member 41 is adaptable to be made relativelylarge to thereby provide a heat sink of relatively large heatdissipating area for the voice coil. For this reason, the voice coilassembly has relatively high power handling capabilities. In addition,such a construction enables the driving surface, i.e. the driving basememher 410, to be relatively large and to provide a relatively largedriving surface over the effective rectangular radiating area of theplanar dia-phram 20. As such, the voice coil assembly 40 together withthe magnetic structure 60, to be described later, result in excellentmeans for driving a relatively large radiating diaphragm 20 whichconsequently has relatively good coupling to the air and hence requiresno special enclosure or baffle. This results in excellent low frequencyreproduction by the loudspeaker.

It has been discovered that the optimum distance between the sides ofthe support 41 and suspension means 30 should be approximately 4 to 5inches, however, depending on the rigidity of diaphragm 20, adequateperformance can be provided if this distance is between two and eightinches. The thickness of the diaphragm 20, for optimum performance wasfound to be in the neighborhood of one-fourth of an inch. However, thethickness of the cellular plastic planar diaphragm 20 could be betweenan eighth of an inch and one inch and still provide suitableperformance.

As shown in FIGS. 1, 3, 4 and 5, there is provided a frame assembly 50which can be made of metal or some suitable other material. Therectangular frame member 50 consists of two horizontally disposedL-members 51 and 53 and two vertically disposed L-members 52 and 54.These L-members are secured at their ends to provide a rectangularpicture frame to which is mounted the edges of the suspension means 30in a rectangular pattern. The supporting L-members 51, 52, 53 and 54have vertically disposed outer flanges 51a, 52a, 53a and 54a,respectively.

The outer planar edges of the suspension means 30 are clamped betweenthese outer flanges 51a, 52a, 53a and 54a and a rectangular clampingplate 55. The rectangular clamp member or frame 55 includes an upperhorizontally disposed plate member 55a, a lower horizontally disposedmember 55c and two vertically disposed clamping sections 55b and 55d.The ends of these clamping sections are integral or secured thereto toform the rectangular clamping assembly 55. Suitable screws which passthrough holes in the clamping assembly 55 into the vertically disposedflanges 51a, 52a, 53a and 54a of the L-members 51 through 54 clamp theouter planar fastening portions 320, 33c, 34c and 350 of the suspensionmeans 30. More specifically, the outer relatively thin portion 320, asshown in FIG. 5, is secured between clamping member 55a and flange 51a.The fastening portion 330 of suspension means 30 is clamped betweenclamping member 5517 and vertically disposed flange 52a. Portion 34c isclamped between clamping member 550 and vertically disposed flange 53a.as shown in FIG. 4, is clamped between vertical flange 54a and clampingstrip 55d. Suitable clamping material, such as rubber or felt, can beemployed between these fastening or terminal portions and frame 55 aswell as between these portions and flanges 51a, 52a, 53a and 54a. Screws56 are applied through the fastening strips 55a, 55b, 55c and 55d,through portions 32c, 33c, 34c and 350 and the vertically disposedflanges. Screws 56 are tightened sufliciently to provide secure mountingof the terminal strips 320, 33c, 34c and 35c.

A magnetic assembly 60 is secured to the side flange 52b and 54b of theL-channels 52 and 54, respectively, by L-members 72 and 71. The magneticassembly 60 provides two horizontally disposed air gaps 69 and for thevoice coil assembly 40, as illustrated in FIG. 2. These two air gaps areadapted to receive voice coil section 43 and 44 of the voice coil 42.

More specifically, the magnetic assembly 60, shown in FIGS. 1 and 2,comprises a rectangular rear pole member 61. The term pole memberhereinafter is meant to mean a non-magnetized member which conducts amagnetic field but in itself is not a permanent magnet. Secured to therear pole member 61 are two rectangular magnets 63 and 64 which areequally spaced on opposite sides of the center of the rear pole member61. These rectangularly shaped magnets are the type on which one side isLikewise, terminal strip 350,

magnetized north and the other side south. As shown in FIG. 1,.themagnetic member 63 has a rear portion 63a which is polarized north withthe front half portion 63b polarized south. Likewise, the magneticmember 64 has a rear half portion 64a polarized north and the front halfportion 64b polarized south. It will be understood that portions 63a and64a may be either north or south, however, they must both be magnetizedthe same. Likewise, the portions 63b and 64b must be polarized in thesame direction, but in the opposite direction to portions 63a and 64a.The portions 63a and 64a are secured by some suitable adhesive to andlongtiudinally of the rear pole member 61. The outer surface of portions63b and 6412 are secured to outer pole members 67 and 68, respectively,for conducting the appropriate magnetic field therethrough. As shown inthe drawing, the rectangularly shaped front pole member 68 isrectangular and has the same shape and dimensions as the magnet 64 withthe edges thereof being coplanar with the edges of the magnet 64. Polemember 67 has three edges coplanar with the edges of magnet 63, but hasone end extending outwardly therefrom.

Secured to the upper edge of the rear pole member 61 is a rectangularlyshaped horizontally disposed top pole member 65. This pole member isplaced, as shown in FIG. 5, perpendicular to the rear pole member 61 andprovides a magnetic linear air gap 69 between pole member 65 and polemembers 67 and 68. This linear air gap is adapted to receive a voicecoil section 43, shown in FIG. 2. The spacing between the ends ofmembers 64 and 68 and members 63 and 67 is sufficiently wide to receivethe supporting strip 41d of the voice coil assembly 46. A rectangularhorizontally disposed lower pole member 66 is secured to the lower edgesof rear pole member 61 and has the same shape and size as the upper polemember 65. As shown in the drawing, the pole member 66 is positioned onrear pole member 61 and perpendicular thereto to provide a surfacespaced from and parallel to the lower edge surface of front pole members67 and 68. This forms lower air gap 76 which is sufficiently wide toreceive the lower voice coil section 44 of voice coil 42. The distancebetween the parallel air gaps 69 and 76 is of course, determined by thedistance between the parallel members 41a and 41b. For optimumperformance it has been found that this distance is approximately 1.5inches. By providing a sufficient distance between members 61a and 41bthe placement of the base member 41c on the rear surface of diaphragm 28is not critical and at the same time provides adequate support foraligning the voice coil with the air gaps 69 and '70 during theoperation thereof. More specifically, by having the driving force fromthe voice coil assembly 40 being distributed or applied to the rearsurface of diaphragm 26 over a relatively large rectangular area,defined by the area of base 410, structural stability of the voice coilis achieved with a relatively uniform force being applied through thisarea so that the exact placement of the voice coil on the diaphragm isnot critical. With the rear diaphragm surface of diaphragm 26 beingsubstantially planar it is possible to have such a relatively largedriving area.

As shown in FIGS. 1, 2 and 6, the pole piece or magnetic conductor 61extends beyond the end of magnet 63 as does the pole piece or magneticconductor 67. As shown in FIG. 6, a circular or cylindrical recess '73is located at the outer side of pole piece 67 at one end thereof. Theother side of pole piece 67 has a reduced thickness area 75'. Extendingthrough this end of pole piece 67 is a circular aperture 74. Mounted, bya screw or other means, on the extended end of pole piece 61 is acylindrically shaped pole piece 76 which extends transverse to polepiece 61 in a position to extend into and coaxial with circular aperture74 of pole piece 67. The pole piece 76 is positioned within the circularaperture 74 and is concentric therewith. Since pole pieces 61 and 67 aremagnetically conducting polarization of opposite magnetic polarity thecylindrically shaped pole piece 76 cooperates with the circular aperture74 to provide a circular magnetic air gap 78. Pole piece 76 has aconically shaped recess 77 at one end thereof. In addition, portapertures 79 are provided through pole piece 67 in recess "73. Thisreduces back loading on the diaphragm of a tweeter 80.

The tweeter 86 is mounted on pole piece 67 and comprises a conventionaldiaphragm having a frustoconical portion 81 which is integral with orsecured to a central dome portion 82 having a single circular surroundconnecting the dome portion 82 and the frustoconical diaphragm 81.Mounted on the diaphragm 81 is a cylindrical voice coil support 83having a conventional cylindrically disposed voice coil winding 84mounted thereon. A cylindrical diaphragm support 86- is secured to polepiece 67 within the cylindrically disposed recess 73 and at theperiphery thereof. The outer edges of the frustoconical diaphragm 81 arerigidly secured by some adhesive to the outer portion of the cylindricaldiaphragm support 86.

The tweeter is dimensioned such that the voice coil 84, cylindrical inshape, is positioned within the magnetic air gap 78 so as to provide thenecessary magnetic air gap for driving the diaphragm of the tweeter, asshown in FIG. 6.

Thus, it is seen that the magnetic assembly 60, in the presentinvention, is utilized not only to drive the larger radiating diaphragm20 to provide reproduction of relatively low notes, but the samemagnetic assembly is utilized to provide a circular or cylindricaldisposed air gap for a tweeter and provide a support for the tweeter. Asuitable crossover network can be provided between the voice coil leads48 of voice coil assembly 40 and leads of the voice coil 84 of thetweeter. The construction of such a crossover network is well known tothose in the art and will not be described in detail.

In order to provide effective radiations of the relatively highfrequencies reproduced by the tweeter 80, apertures 28 are provided inthe diaphragm 20 opposite the tweeter, as shown in FIG. 6 and FIG. 1. Asillustrated in FIG. 6, these apertures are placed in a circular recess27 formed on the back surface of the diaphragm 20. The pic shapedapertures 28 are separated by diametrically disposed reenforcing ribs29. Hence, by employing these apertures the high frequencies radiatingfrom the tweeter 80 will seem to be emanating directly from the largerradiating diaphragm 20. In addition to the magnetic pole pieces of themagnetic assembly 66 being additionally utilized to provide acylindrically shaped air gap for the tweeter the magnetic assembly isbeing utilized to support the tweeter.

The voice coil leads 85 of tweeter 80 are preferably glued to thefrustoconical diaphragm 81 extending outwardly through the connectionbetween cylindrical support 36 and diaphragm 81. The tweeter connections85 extend through a tubular shield 87 and thence through holes 88 on asupporting bar 89. This supporting bar 89, as shown in FIG. 3, ismounted on the rear pole piece 61 to provide a convenient access to thelead 85.

As stated above, the preferred construction and method of fabricatingthe diaphragm 20 is as illustrated in the above-identified patentapplication.

Secured to the ends of the rear pole piece 61 are two L-members 71 and72 for mounting the magnetic structure 66 on the frame 56. Suitableholes in the rear flange of the L-members 71 and 72 are provided whichare secured to the vertically disposed L-members 52 and 54. The magneticassembly is positioned on frame member 52 and 54 so that the voice coilsections 43 and 44 are centrally disposed within the horizontallydisposed air gaps 69 and 70. Additionally, the end voice coil sections45 and 46 are equally spaced from ends of pole piece 67 and pole piece68, respectively. The assembly 60 is positioned over assembly 40 so thatsections 43 and 44 extend into air gaps 69 and 70 a distance such thatthey are centered, depthwise, on front pole pieces 67 and 68, as shownin FIG. 5. This distance between the ends of the voice coil and the endsof the magnet structure is a comprise between tolerance requirements andkeeping the portion of the voice coil that extends beyond the magnetstructure to a minimum since it does not contribute to the performanceof the voice coil. More specifically, this portion of the coil acts as asimple mass, which will effect the frequency response of the unit.

As set forth in the above-mentioned patent application, the diaphragmshould be relatively lightweight, of a material that has a relativelylow Q, yet with an optimum amount of stiffness. It has been found that asatisfactory material, which meets these requirements of constructing arelatively flat or planar diaphragm 20, is foam polystyrene. Othersimilar materials are polyurethane, prefoamed cellulose, polyethylene,acetate, epoxy foams, etc.

The preferred construction and method for manufacturing diaphragm 20 isset forth in the above-mentioned patent application.

Although my invention has been described in considerable detail, suchdescription is intended as being illustrative rather than limiting,since the invention may be variously embodied.

We claim as our invention:

1. A loudspeaker for reproducing audible signals comprising a diaphragm,a first voice coil for driving said diaphragm in response to currentbeing applied thereto, said first voice coil having a linear portion, amagnetic assembly for providing a first voice coil air gap for saidfirst voice coil, including a first magnetic member having a firstpolarity and a second magnetic member having a different polarity, saidfirst and said second magnetic members being positioned on oppositesides of said first voice coil providing a first linear air gap forreceiving said linear portion of said first voice coil, a second voicecoil, a third magnetic member magnetically connected to said firstmagnetic member, a fourth magnetic member magnetically connected to saidsecond magnetic member, said third magnetic member having an aperturetherein, said fourth magnetic member and positioned within said apertureso as to provide a second air gap for said second voice coil.

2. A loudspeaker for reproducing audible signals comprising a firstdiaphragm, a first voice coil for driving said first diaphragm inresponse to current being applied thereto, said voice coil having alinear portion, a magnetic assembly providing a linear air gap forreceiving said linear portion of said first voice coil and including afirst magnetic member having a first polarity and a second magneticmember having a different polarity, said first and said second magneticmembers being positioned on opposite sides of said first voice coil toform said linear air gap, a third magnetic member magnetically connectedto said first magnetic member, a fourth magnetic member beingmagnetically connected to said second magnetic member, a second circulardiaphragm having a second circular voice coil mounted thereon, saidthird magnetic member having a circular aperture therein, said fourthmagnetic member being cylindrical in shape and positioned within saidcircular aperture to form a circular air gap therebetween, said secondcircular voice coil being positioned within said circular air gap, andmeans for mounting the peripheral edges of said circular diaphragm onsaid third magnetic member.

3. A loudspeaker for reproducing audible signals comprising a firstdiaphragm having first and second surfaces which are substantiallyplanar and disposed substantially parallel to each other, a first voicecoil for driving said first diaphragm in response to current beingapplied thereto, said first voice coil having a linear portion, amagnetic assembly providing a linear voice coil air gap for receivingsaid linear portion of said first voice coil, and including a firstmagnetic member having a first polarity and a second magnetic memberhaving a different polarity, a third magnetic member magneticallyconnected to said first magnetic member, a fourth magnetic member beingmagnetically connected to said second magnetic member, said thirdmagnetic member having a circular aperture therein, said fourth magneticmember being cylindrical in shape and positioned within said circularaperture, a second circular diaphragm having a circular voice coilmounted thereon, means for mounting the peripheral edges of saidcircular diaphragm on said third magnetic member with said circularvoice coil being positioned within said circular air gap, and anaperture in said first diaphragm opposite said second circulardiaphragm.

4. A loudspeaker for producing sound signals comprising a firstdiaphragm, a first voice coil for driving said first diaphragm andhaving a rectangular configuration with first and second side portions,a magnetic assembly for providing first and second linear voice coil airgaps for said first and second side portions and including a firstU-shaped magnetic member of a first polarity and having two legportions, a second magnetic member of a different polarity and disposedbetween said leg portions to form said first and second linear voicecoil air gaps, said first and second side portions disposed respectivelywithin said first and second linear voice coil air gaps, a thirdmagnetic member magnetically connected to said second magnetic memberand having a circular aperture therein, a fourth magnetic member beingmagnetically connected to said first magnetic member and beingcylindrical in shape, said fourth magnetic member being positionedwithin said aperture to form a circular voice coil air gap, a seconddiaphragm having a circular voice coil disposed within said circularvoice coil air gap.

5. A loudspeaker as claimed in claim 4, wherein said first diaphragm hassubstantially planar first and second surfaces which are disposedsubstantially parallel to each other, said first voice coil mounted uponsaid first diaphragm for driving said first diaphragm.

6. A loudspeaker as claimed in claim 5, wherein said second diaphragm isof a conical configuration for producing high frequencies.

7. A loudspeaker for reproducing base and high frequencies comprising afirst diaphragm for radiating said base frequencies having relativelyfiat first and second surfaces which are disposed substantially parallelto each other, a first voice coil for driving said first diaphragm andhaving a linear portion, a magnetic assembly for providing a linearvoice coil air gap for said linear portion of said first voice coil andincluding a first magnetic member of a first polarity, a second magneticmember of a different polarity, a third magnetic member magneticallyconnected to said first magnetic member, a fourth magnetic membermagnetically connected to said second magnetic member, said thirdmagnetic member having an aperture therein, said fourth magnetic memberbeing of a cylindrical configuration and disposed within said apertureto form a circular voice coil air gap, at second conically shapeddiaphragm for radiating said high frequencies having a second circularvoice coil, said second circular voice coil being disposed within saidcircular voice coil air gap.

References Cited by the Examiner UNITED STATES PATENTS 5/1958 Manley eta1 l79ll5.5 9/1959 Harris 340-8

1. A LOUDSPEAKER FOR REPRODUCING AUDIBLE SIGNALS COMPRISING A DIAPHRAGM,A FIRST VOICE COIL FOR DRIVING SAID DIAPHRAGM IN RESPONSE TO CURRENTBEING APPLIED THERETO, SAID FIRST VOICE COIL HAVING A LINEAR PORTION, AMAGNETIC ASSEMBLY FOR PROVIDING A FIRST VOICE COIL AIR GAP FOR SAIDFIRST VOICE COIL, INCLUDING A FIRST MAGNETIC MEMBER HAVING A FIRSTPOLARITY OF AND A SECOND MAGNETIC MEMBER HAVING DIFFERENT POLARITY, SAIDFIRST AND SAID SECOND MAGNETIC MEMBERS BEING POSITIONED ON OPPOSITESIDES OF SAID FIRST VOICE COIL PROVIDING A FIRST LINEAR AIR GAP FORRECEIVING SAID LINEAR PORTION OF SAID FIRST VOICE COIL, A SECOND VOICECOIL, A THIRD MAGNETIC MEMBER MAGNETICALLY CONNECTED TO SAID FIRSTMAGNETIC MEMBER, A FOURTH MAGNETIC MEMBER MAGNETICALLY CONNECTED TO SAIDSECOND MAGNETIC MEMBER, SAID THIRD MAGNETIC MEMBER HAVING AN APERTURETHEREIN, SAID FOURTH MAGNETIC MEMBER AND POSITIONED WITHIN SAID APERTURESO AS TO PROVIDE A SECOND AIR GAP FOR SAID SECOND VOICE COIL.